Nowadays, as of 2013-11, Linux systems load a hardware-specific kernel module, to enable general printing support. You need a special kernel module for each different printer( e.g. one module for PCL5, one for EPSON, one for PostScript,..) The printing is then configured by the helpof CUPS.

BusyBox: The Swiss Army Knife of Embedded Linux - “BusyBox combines tiny versions of many common UNIX utilities into a single small executable. It provides replacements for most of the utilities you usually find in GNU fileutils, shellutils, etc. The utilities in BusyBox generally have fewer options than their full-featured GNU cousins; however, the options that are included provide the expected functionality and behave very much like their GNU counterparts. BusyBox provides a fairly complete environment for any small or embedded system”.